PHYSIOLOGICAL ANATOMY OF THE INTERNAL EAR 759 



bounded externally by the periosteum of the corresponding portion of the 

 wall of the cochlea, internally, by the membrane of Reissner, and on the 

 other side, by the membrana basilaris. What is thus called the membranous 

 cochlea is divided by the limbus laminae spiralis and the membrana tectoria 

 into two portions ; a triangular canal above, which is the larger, and a quadri- 

 lateral canal below, between the limbus and membrana tectoria and the mem- 

 brana basilaris. The quadrilateral canal contains the organ of Corti and 

 various complex anatomical structures. The relations of these divisions of 

 the cochlea are shown in Fig. 272. 



The membranous cochlea, as described above, follows the spiral course of 

 the cochlea, terminates superiorly in a blind, pointed extremity, at the cupola, 

 beyond the hamulus, and is connected below with the saccule of the vestibule, 

 by the canalis reuniens. The relations of the different portions of the mem- 

 branous cochlea to each other and to the scalae of the cochlea are shown in 

 Pig. 271. 



Liquids of the Labyrinth. The labyrinth contains a certain quantity of 

 a clear, watery liquid, called the humor of Cotugno or of Valsalva. A por- 

 tion of this liquid surrounds the utricle and saccule, the semicircular canals 

 and the true membranous cochlea ; and this is known as the perilymph of 

 Breschet. Another portion of the liquid fills the true membranous labyrinth ; 

 and this is sometimes called the humor of Scarpa, but it is known more gen- 

 erally as the endolymph of Breschet. The perilymph occupies about one- 

 third of the cavity of the bony vestibule and semicircular canals and both 

 scalae of the cochlea. Both this liquid and the endolymph are clear and wat- 

 ery, becoming somewhat opalescent on the addition of alcohol. The spaces 

 in the labyrinth are directly connected with the lymphatic system. The 

 space occupied by the perilymph communicates with lymphatics, chiefly 

 through the aqueduct of the cochlea, but there is also a communication 

 through the internal auditory meatus, with the space beneath the dura mater. 

 The endolymph passes to the subarachnoid space, beneath the arachnoid cov- 

 ering of the auditory nerve. As far as is known, the uses of the liquid of the 

 internal ear are to sustain the delicate structures contained in this portion 

 of the auditory apparatus and to conduct sonorous vibrations to the terminal 

 filaments of the auditory nerves and the parts with which they are con- 

 nected. 



Distribution of the Nerves in the Labyrinth. As the auditory nerves 

 enter the internal auditory meatus, they divide into an anterior, or cochlear, 

 and a posterior, or vestibular branch. The vestibular branch divides into 

 three smaller branches, a superior and anterior, a middle, and a posterior 

 branch. The superior and anterior branch, the largest of the three, is dis- 

 tributed to the utricle, the superior semicircular canal and the external semi- 

 circular canal. The middle branch is distributed to the saccule. The pos- 

 terior branch passes to the posterior semicircular canal. The nerves distrib- 

 uted to the utricle and saccule penetrate at the points occupied by the 

 otoliths, and the nerves going to the semicircular canals pass to the ampullae, 

 which also contain otoliths. (See Fig. 269.) In each ampulla, at the point 



